Wheel hub units of known type comprise, in general, a stationary outer ring, a flanged inner hub, rotating in use and provided with a flange to support, in use, a vehicle wheel, and are equipped with coupling systems for coupling sealing assemblies to the wheel hub unit, wherein the sealing assemblies are made up of so-called “cassette” seals including a first and a second annular shield mounted facing each other, respectively, on the outer ring and on an interference-fit surface of the flanged hub to delimit from each other an annular chamber within which are arranged a series of sealing lips carried by an annular seal integrally fixed to one of the shields, generally the shield intended in use to remain stationary.
It has, however, been found that the shield mounted on the flanged hub, placed, therefore, close to the wheel support flange, tends, in use, to move axially with respect to the flanged hub itself, because of the deflection of the flange, i.e. because of the deformations to which the flange is subjected by the wheel as the vehicle goes round bends.
This disadvantage on the one hand increases the friction affecting the sealing assembly, since the sealing lips which are not scraping (and therefore not generating friction) can become scraping (and therefore generate friction) and any sealing lips which are scraping increase their interference and, therefore the friction generated. On the other hand, in the case of relatively large movements, it can cause interference between the rotating shield and the stationary outer ring, with very high friction being generated and with possible damage to the sealing assembly, and even, in the most serious cases, to the wheel hub assembly itself.